Sample preparation is a necessary step to facilitate the investigation of failure mechanism in an integrated circuit (IC) chip. The standard procedure involves the extraction of a die from the wafer, coating the die with a layer of protective epoxy and then mechanically polishing the cross-section of the die to the location of interest for inspection using the optical microscope, Scanning Electron Microscope (SEM), Atomic Force Microscopy (AFM) or Transmission Electron Microscope (TEM).
In conventional sample preparation, typically one sample is prepared at a time. While there are some commercial tools that are equipped with multi-sample polishing capability, these systems usually only polish the die in a planar direction. For tools which are able to perform cross-section polishing, these tools require the samples to be molded into a cylindrical form before they could be placed under the polishing head and the molding of epoxy into a cylindrical form requires a longer curing time. These tools are not equipped with level-adjustment capability while performing cross-section polishing.
In the process of the aforementioned molding, it is common to witness the formation of bubbles as the epoxy volume is typically large and air could be trapped as a result. The presence of bubble is undesirable as voids and non-uniformity could be created within the dried epoxy. Moreover, the presence of these voids could affect the ability of the epoxy to hold the internal structure of the sample during mechanical polishing. Besides affecting the support rigidity, the larger volume of epoxy will also take a longer time to be polished away, thus affecting throughput.
Furthermore, in embedding the sample within a thick (diameter of about 1 inch) epoxy cylinder, either the cross-section of the sample is visible but the planar surface would blocked by the thick epoxy or the planar surface is visible but the cross-section is blocked by the thick epoxy. Such poor sample visibility would affect the user's ability to determine if the site of interest has arrived.
From the foregoing discussion, it is desirable to provide a simple, economical and fast setup for multiple-sample cross-section polishing.